When it comes to digital advertising, it's Google's game to lose. But challenger Facebook is putting up a good fight, particularly on mobile where the social network is projected by eMarketer to net nearly 16 percent of a $16.65 billion worldwide mobile ad market this year.

EMarketer, more bullish on Facebook's mobile prospects after a strong second-quarter showing, revised its projections Wednesday to bump up the social network's share of the mobile ad market. The analytics firm, however, still expects Google to bring home the bulk of mobile Internet ad revenues in 2013, pegging the search giant's share at 53.17 percent, or roughly $8.85 billion.

Net mobile Internet ad revenue share worldwide, by company
eMarketer

For its calculations, the firm includes revenue from mobile display and search ads for both phones and tablets, but excludes messaging-based advertising. Figures represent net ad revenues after traffic acquisition costs.

Looking at Facebook's and Google's revenue share side-by-side, the social network's mobile ad grab seems marginal compared to Google's projected more than 50 percent cut. On deeper inspection, however, one notices that Google's anticipated 2013 share will remain mostly flat year over year while the overall ad mobile ad market will inflate by 89 percent this year, according to eMarketer. In 2012, Google earned 52.36 percent of worldwide mobile Internet ad revenue.

Facebook, meanwhile, has better capitalized on the expanding market with its expected 2013 15.8 percent share, which is up significantly from 5.35 percent last year. This comes as no surprise to those following the company's earnings statements. Facebook flabbergasted Wall Street by earning 41 percent of its second-quarter advertising revenue from mobile. The social network, now with 819 million mobile active users, also continues to see increased activity on mobile. Should these trends continue, 2014 will play out as a head-to-head duel between Google and Facebook over share of mobile ad revenue.

On Web, however, Google stands alone, and across all devices -- Web and mobile -- Google is the undisputed leader in digital ad publishing. The search company will take in 32.84 percent of all digital ad dollars worldwide this year, according eMarketer. Second place Facebook will take in just 5.41 percent.